What are external costs?

Famous quotes containing the words external and/or costs:

    It can be fairly argued that the highest priority for mankind is to save itself from extinction. However, it can also be argued that a society that neglects its children and robs them of their human potential can extinguish itself without an external enemy.
    Selma Fraiberg (20th century)

    That which costs little is less valued.
    Miguel De Cervantes (1547–1616)